What GTmetrix measures
GTmetrix runs your page in a real Chrome browser from a test location and reports two things. The Performance score is based on the same Core Web Vitals measurements Google uses. The Structure score is GTmetrix grading how the page is built, so things like image sizing, caching rules and render blocking files. Under both sits the waterfall, a bar chart with one row per request.
How to read your result
The grade at the top is the headline, and the waterfall is where the answer actually lives. Look for long bars, and look for where the bars stop being stacked and start running one after another, because that is a chain of requests waiting on each other. A row that sits mostly in yellow is time your server spent thinking; a row that is mostly purple or blue is time spent downloading. Rows are in the order the browser asked for them, so anything sitting near the top and taking a long time is delaying everything under it.
What to change first
Find the single longest bar in the waterfall and deal with that file. If it is an image, compress it and serve WebP. If it is a font, subset it and preload it. If it is a third party script like a chat widget or a tracking pixel, load it after the page has painted rather than in the head.
Common questions
- Why does GTmetrix give me a different score than PageSpeed Insights?
- They test from different places on different connections. GTmetrix defaults to an unthrottled desktop browser in Vancouver, while PageSpeed Insights simulates a throttled phone. Neither one is wrong.
- What is a good GTmetrix grade?
- An A or B on both Performance and Structure means the page is in decent shape. Chasing a perfect A on a site with real marketing tools installed is usually not worth the effort.
- Do I need a GTmetrix account?
- Not for a basic test. An account lets you pick the test location and browser, which matters if most of your visitors are nowhere near the default server.
Related tests
Run this alongside every other test in Website Speed Tests, or start from the full list of website testing tools.